Can't Add Album Artwork.. Please Help!

Ok, so I have a tivo and use a tivo program to transfer a few shows/movies to my computer and then convert them for itunes. Well I just transferred 1 episode of entourage into my tv shows section of itunes. It will not let me add an artwork to it! Right now it just has a picture of nothing really and I tried to add a new artwork picture but once I hit ok, it just goes right back to the picture of "nothingness." If you have a suggestion, I would really appreciate it! Thanks!

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